The present invention relates to a communication system adapted to perform a mode selection by selecting or negotiating the mode to be used. Furthermore, the invention relates to a method to be performed in such a communication system, and to a network element capable of mode selection.
Advancements in digital communication techniques have permitted increased data transmission rates and introduction of new types of communication services. When digital communication techniques are utilized, data which is to be communicated is digitized into digital form, and sometimes formatted into data packets. The data packets are communicated, either individually, or in groups, to a destination. Once received at the destination, the packets are concatenated together to recreate the informational content of the data of which the data packets are formed.
Radio communication systems are exemplary of communication systems which have benefited from advancements in communication technologies and in which digital communication techniques are increasingly utilized. A cellular communication system is an exemplary radio communication system. And, various standards have been promulgated pursuant to which different types of cellular communication systems have been constructed. Additional standard specifications continue to be promulgated relating both to improvements to existing cellular communication systems as well as new constructions of cellular communication systems. Standards relating to so-called, third-generation, cellular communication systems are presently being promulgated. Standards relating to the 3G (third generation) GSM/EDGE (Global System for Mobile Communications/Enhanced Data for Global Evolution) system, for instance are being promulgated.
In packet switched communications, data to be communicated is formatted into packets, and the data packets are communicated at discrete intervals. Because the data can be communicated at discrete intervals, the communication resources, such as the bandwidth available upon the radio links formed between mobile stations and network infrastructure of the system, can be utilized more efficiently.
Packet-switched communications in which communications are effectuated by the communication of data packets include voice communications. When the data packets are formatted pursuant to IP (Internet Protocol) protocols, the resultant communication service is sometimes referred to as VoIP (Voice over Internet Protocol). As with other types of voice communication services, VoIP is time sensitive in that the data forming the VoIP data packets must be timely communicated to maintain an acceptable communication quality level.
The data packets are typically formatted pursuant to conventional standards. Each data packet is typically formatted to include a header portion and a payload portion. The payload portion is formed of the data which is to be communicated to effectuate the communication service. In a VoIP service, the voice data is contained in the payload portion of the data packet. And, the header portion includes information needed to route the data to a desired receiving station and to identify the order of the data packet amongst a group of data packets. A conventional data packet includes an RTP (Realtime Transport Protocol) header field, a UDP field, and an IP (Internet Protocol) field. The RTP field includes a time stamp value which specifies the time when the voice data of the packet is created. The time stamp is used at a receiving station to correct for delay fluctuation introduced during communication of the data packet. The RTP field also includes a sequence number. The sequence number is used at a receiving station to detect packet loss and mis-sequencing of data packets. Values of the UDP and IP fields are generally of constant values for data packets generated within a single communication session and identify the identities of the sending and receiving stations.
Communication systems are usually bandwidth-constrained. That is to say, the bandwidth available to define communication channels and allocated for use in a communication system typically limit the communication capacity of the communication system. The communication capacity of the communication system can be increased only when the bandwidth allocated to the communication system is used more efficiently. Constraints placed upon radio communication systems are oftentimes particularly acute as the bandwidth allocated to a radio communication system is typically limited to a frequency region of the electromagnetic spectrum.
A problem associated with the use of packet-formatted data is the relatively high percentage of the bandwidth consumed by the communication of the header portions of all of the data packets. Communication of the voice information pursuant to a VoIP communication service is much less efficient than it otherwise would be if the header portions of the data packets are removed.
To increase the efficiency of use of the bandwidth allocated upon the radio link, proposals have been set forth to provide manners by which to remove the header portions of the data packets prior to their communication upon the radio links formed between mobile stations and the network infrastructure of the communication system.
More generally, communication networks transfer information such as user voice traffic or the like, on a packet-switched and/or circuit-switched basis using modes which may be commanded by the system or negotiated between the involved network elements such as end user equipments. As an example, in evolved networks such as UMTS (Universal Mobile Telecommunication System) systems, additional functions and services can be incorporated. For instance, novel multimedia services such as multimedia messaging services MMS are supported within the system which services are IP (Internet Protocol)-based services. Packet-based (e.g. IP-based) service sessions such as multimedia service sessions may be controlled by a specific protocol. As an example, the Session Initiation Protocol (SIP) represents a protocol which may be used e.g. for call and connection establishment as well as for transport of endpoint capability information. Such capability information may e.g. relate to voice and multimedia codecs supported by the end terminals.
The functionality and services of such multimedia service systems will be mapped onto the existing network system functions, e.g. of UMTS type. As an example, the system services may be mapped to the PDP contexts and radio signalling, as well as to existing packet-switched core network elements and interfaces, e.g. of UMTS type. Hence, there is a problem of multimedia (e.g. IP multimedia) and network layer (e.g. GPRS layer) interactions and mapping.
As an example, in case of VoIP calls (voice over IP-based connection, i.e. Internet telephony), the radio access network such as GERAN (“GSM/Edge Radio Access Network”) and UTRAN (UMTS Terrestrial Radio Access Network), may be informed on the type of application for deciding on the header adaptation method to be used for e.g. a particular PDP context. As an example, two different header adaptation schemes available for selection can for example be “header compression” and “header stripping/removal”. The header stripping/removal mode may be used for speech-only traffic where e.g. optimised speech transport is required for instance for integrated lower-end terminal devices. A header compression mode may be utilised e.g. for more general IP multimedia traffic including voice application operation on an external device such as a laptop computer connected to a UMTS phone.
When an inappropriate mode such as inappropriate protocol mode, header adaptation mode or radio access bearer mode should be selected, problems in incorrect message transmission may occur.